Some Considerations about the Sensing Mechanisms and Electrical Response of Carbon Nanohorns-based Gas Sensors

This paper aims to analyze the sensing mechanisms involved in the resistive detection of relative humidity, ethanol vapors, oxygen, ozone, ammonia, hydrogen sulfide, and hydrogen using carbon nanohorns (pristine and functionalized) and their nanocomposites/nanohybrids as sensing layers. Different alternative mechanisms are considered and discussed: decreasing holes in the carbonaceous component at the interaction with moisture, protonic conduction (Grotthuss mechanism), and swelling. The hard-soft acid-base (HSAB) theory's role is also highlighted as a valuable tool for understanding the essential interaction of nanocarbon materials with water molecules. The role of each constituent of the sensing layer is interpreted based on their chemical and physical properties and mutual interactions. For each tandem sensing layer - gas detected, the dominant sensing mechanism is associated with the electrical response of the sensor.